1. Technical Field
The present disclosure relates generally to a discharge lamp system, and more particularly to a discharge lamp system in which a constant power control of a discharge lamp is performed. The present disclosure relates also to a controlling method for the discharge lamp system.
2. Description of Related Art
Conventionally, high intensity discharge (HID) lamps have relatively high efficiency, good color rendering, and a long service life, such that HID lamps are widely used in many applications.
However, an HID lamp is a relatively complex load, and the parameters (voltage, current and power) of the discharge lamp are often changed within an operation time period. A waveform diagram of a typical procedure for controlling a discharge lamp is shown in FIG. 1. When the discharge lamp is operated at a raising stage after the discharge lamp is ignited, the discharge lamp is operated under a constant current mode, and a discharge lamp power will increase gradually (at a constant current stage) with an increasing discharge lamp voltage (Vlamp). For acquiring a better discharge lamp performance, when the discharge lamp voltage is greater than a first predetermined value V1, a constant power control stage is entered, where the discharge lamp voltage will continue rising until a lamp impedance has a stable value. At this moment, the discharge lamp power is adjusted under an operation of a constant power. Over the lifetime of the discharge lamp, the lamp impedance of the discharge lamp will increase with an increasing lamp operating time, and thus the discharge lamp voltage will rise with the increasing lamp operating time. However, the discharge lamp power is controlled so as to have a constant value.
Usually, the discharge lamp voltage (Vlamp) and a discharge lamp current (Ilamp) are detected directly for the constant power control of the discharge lamp by a computation process when the discharge lamp is operated at the constant power stage. However, Vlamp and Ilamp are difficult to directly detect in some real-life applications, and thus it is a challenge to perform constant power control of the discharge lamp by detecting Vlamp and Ilamp directly.
Furthermore, in other applications of the discharge lamp, such as in a projector system, the discharge lamp can emit different colors of light based on different lamp currents. As shown in FIG. 2, discharge lamp voltage (Vlamp) and discharge lamp current (Ilamp) waveform diagrams are shown within a specific time period. It can be seen that the discharge lamp voltage and the discharge lamp current are continuously transitioning and they are unable to be maintained at a constant value. Under such conditions, if constant power control is performed directly for the discharge lamp, accuracy issues will be encountered.